This invention relates to a fuel injection control system for an internal combustion engine and more particularly to an improved control system and routine for controlling fuel injection in a two-cycle engine.
In an internal combustion engine, it is important to accurately control the amount of fuel injected to the engine to improve fuel economy. A wide variety of types of controls for fuel injection for internal combustion engines have been proposed. These controls generally sense one or more engine parameters and then set the amount of fuel injected in response to the sensed parameters. This setting is normally done by the measuring of the running conditions and then the selection of the fuel injection amount from a map generated from actual running condition. Although these systems are generally quite accurate, they do have some disadvantages.
For example, one parameter that is frequently measured in a two-cycle engine is air flow to the engine. There are various types of air flow sensors which have been employed. One way of measuring the air flow for controlling the fuel injection measures air pressure in the crankcase chamber at different times and derives the air flow from the pressure differences. The amount of fuel injected to the engine is controlled depending on the crankcase pressure detected by a pressure sensor installed in the crankcase.
This method of sensing the crankcase pressure can be quite accurate under many running conditions. However, its accuracy can be not as good as other types of devices under other running conditions. As a result, the amount of fuel supplied under the conditions when the measuring device is not as accurate will also be inaccurate. One of the factors that deteriorates the accuracy resides in the fact that the intake air may include water vapor and/or vaporized fuel such as gasoline. As a result, the measured crankcase pressure by the pressure sensor includes pressure components based on the water vapor and the vaporized fuel other than the intake air pressure to be measured.
Thus, in the conventional system of measuring the crankcase pressure, it is not possible to accurately control the fuel injection. In the crankcase pressure measurement to determine the intake air pressure, the crankcase pressure is measured at two different times. One measurement is performed at the time of starting scavenge (scavenge port opening timing) and the other measurement is performed at the time of ending the scavenge (scavenge port closing timing). The intake air pressure will be calculated based on these two measurement results.
In these measurements, however, an impulse-like pressure caused by an exhaust gas pressure may sometimes comes in the crankcase chamber through a cylinder and a scavenge path. Such an impulse-like pressure of the exhaust gas may derive from the cylinder associated with the crankcase member which is being measured but also from the other cylinders. Especially, this pressure caused by the exhaust gas pressure in the cylinders affects the crankcase pressure measurement at the end timing of the scavenge. As a result, depending on the detection timing, it is difficult to obtain accurate air pressure data, and thus, it is difficult to accurately control the fuel injection.
Further, in the crankcase pressure measurement, it is necessary to install a pressure sensor in each cylinder to measure the intake air with high accuracy. As a consequence, in an engine having a large number of cylinders, for example, six cylinders, six pressure sensors have to be installed. However, such a large number of pressure sensors makes the structure of the system and the process for measuring the intake air complicated. In case where one or two pressure sensors are installed to measure other cylinders, accurate measurement is not possible since the crankcase pressure and intake air are different from cylinder to cylinder. As a result, it is not possible in the conventional crankcase pressure measurement to precisely control the fuel injection. Furthermore, in the two-cycle engine, a misfire wherein one or more cylinders fail to fire will sometimes occur. In such a situation, the crankcase pressure is affected by the misfire and thus it is difficult to accurately control the fuel injection solely based on the crankcase pressure measurement.
It is, therefore, a principal object of this invention to provide an improved fuel injection control system that is capable of accurately control the fuel injection by measuring the crankcase pressure with high accuracy incorporating the intake air condition.
It is a further object of this invention to provide a fuel injection control system for an engine that is capable of measuring the crankcase pressure without being affected by an exhaust gas pressure.
It is a further object of the present invention to provide a fuel injection control system for an engine which is capable of simplifying the structure and calculation process for measuring the intake air.
It is a further object of the present invention to provide a fuel injection control system for an engine which is capable of detecting a misfire of a certain cylinder and compensating for the effect of such a misfire in measuring the crankcase pressure to accurately control the amount of fuel injection to the engine.